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The field of this invention is that of liner hangers for the isolation of the well bore of oil and gas wells from the earth formations through which the oil or gas well is being drilled.
As different producing formations which the drilled well will pass through must be isolated from each other, a casing string must be cemented in place to isolate each zone. An oil or gas well is typically drilled by first deciding the minimum bore of the production string of casing, or the last pipe to be cemented in place, and which will be continuous from the surface all the way down to the oil or gas producing formations. This production string of casing must be large enough to allow the production tubing landed inside it to flow enough oil or gas at sufficient volumes to make the well economic.
Each casing set point requires that an additional concentric casing string be set. A typical set of casing strings in a subsea environment from the inside out would be 7xe2x80x2, 9.625xe2x80x3, 11.750xe2x80x3, 13.375xe2x80x3, and 16xe2x80x3 set within an 18.750xe2x80x3 bore blowout preventer stack, 20 and 30xe2x80x3 casing strings set before the 18.750xe2x80x3 bore blowout preventer stack is installed. Each casing string occupies a certain amount of radial space, requiring that the next string of pipe be progressively smaller. That program provides a maximum of 5 casing set points with blowout preventer protection during drilling.
Typically, a casing string, i.e. 11.75xe2x80x3 outer diameter, is installed in, a drill well bore suspended from the surface to a depth such as 10,000 foot depth. After cementing the 11.750xe2x80x3 casing in place, a hole is drilled with a bit through the 11.750xe2x80x3 casing, i.e. 10.50xe2x80x3 diameter hole to 12,000 feet deep. Into this hole a 9.625xe2x80x3 outside diameter casing can be landed and cemented in place. If the 9.625xe2x80x3 casing string is suspended from the surface and is therefore 12,000 feet long, it is called a casing string. If, however, the 9.625xe2x80x3 casing is only 2000xe2x80x2 long and is suspended by a hanger from the lower end of the 11.750xe2x80x3 casing string, it is called a liner. The use of a liner can save substantially on the cost of casing and cement, e.g. 10,000 feet of casing not purchased. The well program would be followed with a 7.000xe2x80x3 casing string continuous from the surface to the bottom of the well as the production casing string.
The 9.625xe2x80x3 liner in the example above would have saved the operator the 10,000 feet of casing not purchased, with the cost of a conventional liner hanger being generally offset by the cost of the surface casing hanger. The liner still xe2x80x9ccostsxe2x80x9d the drilling company the xe2x80x9cradial spacexe2x80x9d, forcing the next string to be progressively larger.
In this conventional scenario, if an unexpected pressured formation is encountered and requires that an extra casing string be set, it would probably be 5.500xe2x80x3 in outside diameter. With the 5.500xe2x80x3 size, the tubing string landed inside would be reduced from 3xe2x80x3 to 2xe2x80x3, substantially restricting the flow of production from the well. Flow from wells is especially important offshore where the high cost of drilling and producing wells demands a high flow rate to be economic. Cases have been seen of abandonment of wells when an extra pressurized reservoir zone was encountered and the driller realized that his final well bore size would be too small to be economic.
Other methods, such as described in U.S. Pat. No. 6,435,281 provide for the ability to utilize liners which offer characteristics such as are listed in liners above, with the additional feature that they expand below the casing string they attach to. This means that the well bore will not be reduced a stage, making either the ultimate hole larger, or allowing one to start with a smaller string at the top. This style provides a feature that a substantial length of the liner could be rolled up on a reel and simply unrolled into the well bore for inflation. A disadvantage of this style was that during the unrolling and running operation, it was of a shape which could not be sealed on by blowout preventers to maintain well control. It depended upon having a xe2x80x9cdeadxe2x80x9d well, or one in which the pressure head of the liquid mud column in the well bore exceeded the formation pressures. This can be of particular advantage when an actual application of the liner is to seal off an unexpected pressure zone in the formations.
The object of this invention is to provide a liner which does not occupy xe2x80x9cradial spacexe2x80x9d in the well bore and therefore does not force each previously set casing hanger to be a step larger in diameter.
A second object of the present invention is to provide the capability of installing multiple liners in a drilling program to compensate for unforeseen well control situations.
A third object of the present invention is to provide a liner that can be rolled up for compact storage and shipment.
Another object of the present invention is to provide a liner assembly that is compact enough to be airlifted out to an offshore drilling vessel.
Another object of the present invention is to provide an expandable liner that is metallic in construction and impervious to fluid flow.
Another object of the present invention is to provide an expandable liner which can be sealed upon with a blowout preventer to provide well control during the running operations.
Another object of the present invention is to provide an expandable liner which can be supported by smooth face wedge slips which eliminate the need for marking the liner with sharp slip teeth.